1 Technical Field
The present invention relates to stators for electric rotating machines that are used in, for example, motor vehicles as electric motors and electric generators, and to methods of manufacturing the stators.
2 Description of Related Art
Conventionally, there are known stators for electric rotating machines which include a hollow cylindrical stator core and a stator coil.
The stator core has a plurality of stator teeth and a plurality of slots. The stator teeth each extend radially inward and are spaced from one another in the circumferential direction of the stator core at predetermined intervals. Each of the slots is formed between a corresponding circumferentially-facing pair of the stator teeth so as to open at the radially inner periphery of the stator core. In addition, to reduce the iron loss, the stator core is formed by laminating a plurality of stator core sheets in the axial direction of the stator core; each of the stator core sheets is blanked out of a magnetic steel sheet so as to have a predetermined shape. The stator coil is comprised of a plurality of electric wires that are mounted on the stator core so as to be received in the slots of the stator core.
With the above configuration, however, the electric wires may be caused, for example by external vibration transmitted to the stator, to protrude radially inward from the slots of the stator core, thereby interfering with a rotor of the electric rotating machine which is disposed radially inside of the stator.
Japanese Patent Application Publication No. 2010-239721 discloses a technique for solving the above problem. According to the technique, as shown in FIG. 15A, each of the stator teeth 134 has a pair of radially-extending protrusions 136 formed at the distal end thereof. The radially-extending protrusions 136 each extend radially inward with a circumferential gap formed therebetween. After the electric wires that make up the stator coil are received in the slots 131 of the stator core 130, each of the radially-extending protrusions 136 is bent toward an adjacent one of the slots 131, thereby being transformed (or altered) into a circumferentially-extending protrusion 137 as shown in FIG. 15B. Consequently, for each of the slots 131 of the stator core 130, the opening of the slot 131 is partially closed by a corresponding pair of the circumferentially-extending protrusions 137; thus, the circumferential width of the opening becomes smaller than that of the electric wires received in the slot 131. As a result, the electric wires are prevented from protruding radially inward from the slots 131 of the stator core 130.
However, with the above technique, in forming the stator core sheets of the stator core 130 by blanking them out of a magnetic steel sheet, as shown in FIG. 16, those parts 136A of the magnetic steel sheet which will make up the radially-extending protrusions 136 of the stator teeth 134 protrude from a reference line L; the reference line L represents an inner-diameter surface of the stator core 130. Consequently, due to the protruding parts 136A, it is difficult to secure a high yield rate of the stator core 130, thereby making it difficult to minimize the manufacturing cost of the stator.
Moreover, with the above technique, for being transformed into the circumferentially-extending protrusions 137, the radially-extending protrusions 136 of the stator teeth 134 are bent almost at 90°, thereby inducing residual stress in the stator core 130. The residual stress will deteriorates the magnetic characteristics of the stator core 130, thereby lowering the efficiency of the electric rotating machine.
Furthermore, due to springback of the circumferentially-extending protrusions 137, there may be generated minor gaps 137A between the main bodies of the stator teeth 134 and the circumferentially-extending protrusions 137 (see FIG. 15B). Consequently, due to the minor gaps 137A, the torque of the electric rotating machine would be lowered and the iron loss of the stator core 130 would be increased.